conf: don't use "class" as name

conf: don't use "class" as name

Vim treats *.h files as cpp ones with respect to syntax highlighting.
Thus "class" in _virNodeDevCapPCIDev highlighted mistakenly.
This can be fixed by filetype detection code tunables but it
is more convinient to skip this tuning by every project member.

Let's just use "klass" as field name instead of _class or class
and add syntax rule.

Signed-off-by: Nikolay Shirokovskiy <nshirokovskiy@virtuozzo.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>